In medical technologies, innovative implantable electronic devices have become relatively common, yet provide invaluable improvement to the lives of patients. These devices can perform, improve, or control anatomical functions ranging from hearing, pain suppression, appetite control, urinary continence, and cardiac rhythms, among others.
A requirement of an implantable device is that the device be well sealed to prevent bodily fluid from passing into the device interior after implantation, which would allow the fluid to interfere with electrical functioning of the device. Sealing an implantable device can be a relatively simple achievement, by itself. But implantable devices typically require one or more lead connections that are used to connect an electronic lead to an electronic processor. For case of use and the ability to replace individual components of an implantable device, components of an implantable lead connection are separate pieces of an implantable device and are typically connected by a surgeon during a surgical procedure. The lead connection cannot be pre-sealed before implantation, but must instead be assembled during surgery in a manner that results in an impermeably sealed connection that is also mechanically secure and reliable. The need to connect the electrical lead components during surgery to produce a well-sealed connection creates certain challenges, because a surgeon should not be overly burdened with complicated tasks required to secure the sealed connection, during a surgical procedure.
A standard component of a sealed connection is a gasket. A known disadvantage of a sealing gasket is that a gasket can trap air inside of a connection and produce a pressurized interior. Air contained in a channel of a lead connection is held in the channel by the gasket and becomes compressed as the lead terminal is advanced within the channel. A first undesired effect of air becoming trapped by a gasket upon making a connection is an increased insertion force. A more serious effect can be pressurization of the air contained in the channel as the lead terminal is inserted. The pressurized lead channel can tend to push against the inserted lead terminal in a manner that may potentially cause the lead terminal to move within the channel after implantation, e.g., to be dislodged or pushed out of a fully-inserted position within the channel by being at least partially moved within or partially separated from the lead channel. As a practical matter the connection—due to the pressurized air within the lead channel—is less secure than necessary for an implanted device.
The implantable lead connection must be sealed to prevent leakage of fluid into the device and, preferably, to prevent any leaking of electrical current or signal between two or more electrical contacts within the implanted device, or between any one of multiple electrical contacts of an implanted device and the environment external to the implanted device and internal to the patient. Gaskets mounted between a lead terminal and a lead channel are typically used to create the seals between electrical contacts of a single lead connection, and also between the contacts of a lead connection and the patient anatomy.
Overall, the sealed implantable lead connection, with a lead terminal fully-inserted in a lead channel, must be both sealed and secure for an extended time in an environment of a patient anatomy with attendant bodily fluids. Secure means that the lead connection, once completed during a surgical procedure, is sufficiently secure to not subsequently fail within the patient, e.g., to not separate or decouple to any functional extent after surgical placement of the implant in a patient. As a practical matter, the connection must be sufficiently secure that the connection does not stand an unacceptably high risk of failing at any time following surgery. Sealed as a practical matter means that the connection does not fail, malfunction, or produce detrimental functionality due to leakage of fluid into the interior of the lead connection or the implanted device.
According to past and present designs, implantable lead connections have been used that avoid or overcome the problems resulting from a gasket seal and pressurized lead channel, using at least two different or complementary approaches. One approach has been to alleviate the increased pressure within the lead channel by venting the lead channel during or after fully inserting a lead terminal into a lead channel. A second approach has been to mechanically secure the lead terminal in place within the lead channel, after full insertion, using a mechanical device to produce a frictional force that prevents subsequent movement, i.e., a mechanical securing or locking device that produces a force that is sufficient to overcome the force of the pressurized lead channel interior and prevent any subsequent movement of the lead terminal (e.g., slight separation) after implantation, even if the internal pressure remains.
One example of a previous design is found in U.S. Pat. No. 7,305,267. That document shows an implantable connector that includes a “lead retention element” such as screw port or “set screw,” which is also vented, extending through an opening in a sidewall of a connector module of an implantable lead connection. The set screw design performs a venting function because the threaded bore in which the set screw is seated will allow for passage of air from a lead channel to an exterior. The set screw also performs the function of a locking mechanism by placing a lateral holding force on the lead terminal within the channel.
Because a threaded bore opening that holds the set screw at the channel wall will necessarily allow for at least some amounts of fluid and electrical leakage, a seal in the form of a polymeric cover must be in place over the bore and the set screw before implantation. A typical vented set screw port has a silicone diaphragm or “self-sealing” membrane placed over the set screw. The diaphragm can include a small “slit” opening or may otherwise allow a screwdriver to pass through to allow the set screw to be turned and tightened, also allowing air to escape the channel during insertion. Upon removal of the screwdriver, the membrane in its natural state is considered to close and to produce a “seal” that is useful to prevent fluid flow and provide electrical isolation. In practice, however, these self-sealing membranes always include a small slot or opening through which at least a minor amount of fluid and electrical leakage can occur.
In use, this set-screw and self-sealing membrane are not adequate for all types of implantable electronic devices. The design may perform well for pacemaker devices, for example, which do not require relatively high levels of signal detector sensitivity, or high fidelity signal processing or delivery. But a vented set screw design and self-sealing membrane do not provide adequate electrical isolation for implants that do require highly sensitive and high fidelity signal processing, as do, for example, hearing implants. A “self-sealing” membrane does not completely seal. In a hearing implant, an eventual result of the imperfect seal is fluid and electrical leakage at the site of the set screw, allowing electrical leakage either between two electrical contacts of the implant or between an electrical contact and the patient environment. The amount of electrical leaking can result in electrical feedback between an input and an output of the electronic device, which can impact the performance of a hearing implant or other implantable device that requires a high sensitivity or high fidelity input or output signal.
Another example of a previous lead connection design that involves venting a lead channel is found in U.S. Pat. No. 6,039,685. This vented design includes a vent that is closed or covered by a “self-sealing resilient plug.” During or after inserting a lead terminal into a lead channel, the channel is vented by passing a “non-coring” needle through the resilient plug. Like the “self-sealing” set screw design, this design also allows for potential leakage of fluid through the opening made in the resilient plug by the “non-coring” needle. Another disadvantage is that during surgical placement, this design requires a surgeon to perform the step of passing the non-coring needle through the plug to vent the channel.
Still another example of a vent design is a vent between an outer lead terminal surface and an internal lead channel wall, at a location of a sealing gasket during insertion of the lead terminal. Air can be vented from the lead channel during insertion by placing a small tubular structure (e.g., a polytetrafluoroethylene (PTFE) tube) inside of the channel at an inner channel wall, e.g., as a part of the manufacturing process. During surgery, when a lead terminal is inserted into the channel that contains the PTFE tube at an inner surface, the PTFE tube creates a gap at the gasket between the inner wall of the bore and the lead terminal. The gap in the gasket allows air to escape the gasket near the PTFE tube during insertion. After the lead terminal is fully inserted, the PTFE tube can be removed, causing the gasket to fully seal the lead channel from the exterior environment, providing electrical isolation and a fluid-tight seal. A shortcoming of this design is that it requires added steps for a surgeon.
Another potential shortcoming to the these previous lead connector designs is that in use they can lack consistency or reproducibility in venting a channel. For example, when using a PTFE tube to allow air to escape from a channel, a surgeon may not always be certain that the tube was correctly placed, or was effective to remove a necessary amount of air from the channel; but after placement of the lead in the channel and removal of the tube, in the event of doubt on the effectiveness of the vent, a surgeon would have great difficulty separating the lead from the channel and reconfiguring the tube to make a second attempt. If doubt were present as to the effectiveness of the tube to vent the channel, the surgeon would have little choice but to continue with the implantation procedure without knowing for certain that the channel does not contain potentially excessive pressure, or to scrap the unit and complete the surgery using a secondary device.